A Stirling engine is typically characterized by a continously operating external heating circuit which transfers heat to an internal or closed working circuit, the latter typically employing hydrogen at extremely high pressures. The closed working fluid circuit is thermo-dynamically cycled requiring the input of heat from said external circuit and the extraction of heat by a cooling system. In order for the engine to operate for automotive purposes, the average cooling temperature must be maintained at about 60.degree. F. This low temperature is in very abrupt contrast with the much higher temperature of the coolant tolerated in internal combustion engines, the latter being typically about 180.degree. F.
The lower average coolant temperature for Stirling engines presents certain problems for the automotive designer in providing for passenger comfort. Waste heat units for such an engine must be utilized in a different manner than known by the prior art with internal combustion engines, if the passenger compartment is to be consistently heated during periods when heating is required. If a conventional heating system were to be utilized in connection with a Stirling type engine for purposes of heating the passenger compartment, there would be insufficient heat for passenger comfort, since the coolant would be conveyed directly to a heater core in the passenger compartment and would not have sufficient temperature to heat the air flowing therepast to provide for proper comfort.
One prior art attempt to overcome this problem has been to extract heat units from the exhaust gas of such Stirling engines and transfer such heat units to the air supply in the passenger compartment. However, at low road load conditions, there is insufficient heat units from the exhaust to again properly heat the air being supplied to the passenger compartment to a proper comfort level.